Saccade Control in Dyslexia: Development, Deficits, Training and Transfer to Reading
Authors: Burkhart Fischer, Dipl Phys; Klaus Hartnegg, Dipl Phys.
Organization: Centre of Neuroscience, Optomotor Laboratory, University of Freiburg
Journal: Optom Vis Dev 2008:39(4):181-190Abstract:
Background: Saccade control is a complex function of our brain and relies on the coordination of several subcortical, cortical, and functional areas. In the past it has been difficult to use data from saccade analysis as an additional diagnostic tool for insight into any particular patientís oculo-visual problem. With the development of technological advances and optomotor research there is now a better understanding of visually guided saccadic reactions. This article describes the development of saccade control, diagnostic data from dyslexic subjects, and the effect of daily saccadic and fixation practice and its transfer to reading skills.
Methods: All subjects were recruited from local schools. Several standard tests (reading, spelling, intelligence) were used for inclusion/exclusion of the subjects participating in the various studies. Eye movements were recorded by infrared light reflection methods. Prosaccades with overlap conditions and antisaccades with gap conditions were required in 200 trials for each task. Variables characterizing pro- and antisaccade performance were extracted for each subject. Mean values and standard deviations comparing the experimental and control subjects were calculated in each of the 4 age groups in an age range of 7 to 17 years. ANOVAs or t-test were used for statistical evaluations.
Results: The data from 114 normal control subjects show a developmental progression lasting until adult age. Among the 3230 subjects in the dyslexic group 20 to 70% (depending on age) failed the criterion of the age matched controls when looking at anti-saccade performance. Pro-saccade performance did not differentiate between the groups. Daily practice conducted by 182 dyslexic subjects improved their antisaccade performance in approximately 80% of the cases. For training subjects, it was noted that successful training transferred to the act of reading by reducing the percentage of reading errors in the experimental group (N=10) by 50% and by 20% for the control group (N=11).
Conclusion: This study suggests that deficits in antisaccade control but not in prosaccade control contribute systematically to the problems of subjects with specific deficits in acquiring reading skills and that appropriate training can reduce the percentage of reading errors.
Key Words: Eye Movement, prosaccade, antisaccade, oculomotor development, optomotor, optometric vision therapy, dyslexia, reading disabled, EZ-reader model
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